| Emulsion system of polyunsaturated fatty acid (PUFA) has important appliance in food, health, cosmetic, feed and leechdom/drug. Autoxidation proceses of bulk lipid seems clear. However, the oxidation mechanism and factors that influence oxidation are appreciably different for lipid in emulsions than for bulk lipids. A number of reports have appeared in the literature concerning the relations between the interfacial characteristics of emulsion, droplet characteristics and lipid oxidation in emulsions, no general mathematical models for oxidation mechanism and dynamics, and have been presented yet to simulate these data. The studies on the oxidation of PUFA in emulsions were very important for the cortrol of oxidation of PUFA in emulsions and appliance in fields of food, and leechdom/drug theoretically and practically.There are some kinds of environment of emulsion system of food, health and cosmetic as follows: one is close system without gas-phase and without oxygen compensation from atmosphere. Two is close system with limited oxygen compensation (stirring and static state ). Three is open system with infinite oxygen compensation at constant surface oxygen pressure (stirring and static state).Models of diffusion-oxidation were established by logical assumptions and considering the mass transfer resistance of gas-liquid boundary, the diffusion in liquid , the mass transfer resistance of boundary layer from emulsifier membrane, and the autocatalytic-type autoxidation reaction of PUFA compositely in this paper. The oxidation rule of PUFA in emulsions was studied. Differential equations are numerically solved by Runge-Kutta method. The model was verified by comparing the predictions of the model to the experimental data.Model: The oxidation of PUFA in emulsion without oxygen compensation from atmosphere was studied. The equations are composed of oxygen diffusion and PUFA oxidation in droplet. Mass transfer coefficient of emulsifier membrane k0 was obtained by mathematics experiment. The results indicated that the model is consistent well with the oxygen diffusion and linoleic acid oxidation in emulsion, and showed that the oxid- ation of PUFA in emulsion without oxygen compensation from atmosphere was controled by mass transfer resistance from emulsifier membrane and the specific surface area of oil phase to aqueous phase. Modelâ…¡: The oxidation of PUFA in emulsion with stirring and infinite oxygen compensation at constant surface oxygen pressure was studied. An mass tranfer equation of gas-liquid boundary was added based on modelâ… . The results showed good applicibility in the prediction of the effect of emulsifier concentration, structure and concentrations of PUFA etc on the oxidation of PUFA in emulsions. Decreasing emulsifier concentration , or initial concentration of PUFA led to an increase in total oxidation of PUFA . Temperature and structure of PUFA had little effect on oxidation of PUFA. Another model of oxidation of PUFAs in their mixed system was established. The results indicated that the oxidation of one of PUFA was promoted as its content in the mixture increased.Modelâ…¢: The oxidation of PUFA in emulsion with stirring and limited oxygen compensation was studied. Dynamic mass tranfer coefficient of emulsifier membrane k0 was induucted. This model showed good applicibility in the prediction of the effect of emulsifier type, structure and concentration of PUFA, oxygen press on the diffusivity of oxygen and oxidation of PUFA in emulsion. A rapid check way of oxygen was established by press difference of U-shape manometer.Modelâ…£: The oxidation of PUFA in emulsion with static state and infinite oxygen compensation was studied. A diffusion-oxidation model with partial differential equation (PDE) was established by consider- ing the mass transfer and autocatalytic-type autoxidation of PUFA synthetically. Complex boundary was deal with distinguishingly and the PDE were numerically solved by orthogonal collocation method of dissymmetry. The oxygen diffusivity of liquid-phase was obtained by mathematics simulation and experimental data. The model showed good applicibility in the prediction of effect of concentration of PUFA etc on the oxidation of PUFA in emulsion.Oxidation of PUFA in emulsion systems for some kinds of condition were studied roundly in this paper. By considering the mass transfer resistance of gas-liquid boundary, the resistance of boundary layer from emulsifier membrane, diffusivity of liquid-phase and the autocatalytic-type autoxidation reaction of PUFA compositely, four kinetics models of diffusion-oxidation were established with innovation. these four models were based on system with closed without oxygen compensation from atmosphere, or agitating and infinite oxygen compensation at constant surface oxygen pressure, or agitating and limited oxygen compensation, or static state and infinite oxygen compensation at constant surface oxygen pressure. and which showed good applicibility in the prediction of effect of emulsifier type and concentration, PUFA structure and concentration, oxygen pressure, and temperature on oxygen distributing and PUFA oxidation in emulsions for some conditions roundly.It is confirmed that the oxidation of PUFA in emulsions is heterogeneous reaction, oxygen diffusion during gas-liquid-liquid , and the effect of diffusivity on oxidation of PUFA is more important for lipid in emulsions than for bulk lipids. The process of oxygen diffusion and oxidation of PUFA was expressed completely by four models. Oxidation mechanism of PUFA in emulsions was that the oxidation is controled by mass transfer mainly, which is cooperated with three kind of mass transfer. |
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